This invention relates to catalytic converters useful in motor vehicle exhaust gas systems and, in particular, to converters of the type having one or more ceramic monoliths or substrates mounted inside of a sheet metal housing, the substrates containing a multiplicity of longitudinal straight-through-flow exhaust gas passages that are coated with catalyst. Such catalytic converters are intended for installation on motor vehicles as original equipment by the vehicle manufacturer or as aftermarket replacement for original equipment converters.
Typically, the metal housings for commercially acceptable converters of the type just described are of the so-called "pancake" or "clamshell" design; i.e., they comprise stamped upper and lower shells, which are substantially identical to each other, and which have mating, peripheral, side flanges that are welded together to lie in a plane containing the longitudinal axis of the housing. They are shaped to form an internal chamber in which the substrates are mounted by "L-shaped" or other known brackets. Another commercial form of catalytic converter housing comprises a tube with separate end cones welded at each end; i.e., a three-piece housing.
It is a purpose of the present invention to reduce the size and number of parts in a catalytic converter (as compared with known practical constructions) while at the same time increasing its effectiveness and improving its construction and manufacture. The present invention achieves the foregoing purpose by means of a substrate support in the form of a tubular converter body which is reduced in diameter at a central portion to compress a support mat around a catalyst substrate. Such substrate support provides a construction and manufacture that results in a converter that is relatively short in length, has few parts, has maximum effectiveness since 100% of the substrate end faces can be used, and has improved accuracy in supporting the substrate.
It is also a purpose of the present invention to provide a converter of the type described above, and the method of making it, which has a one-piece, metal, tubular housing instead of a two-piece "clamshell" housing or the three-piece end cone type housing. A converter according to the invention performs at least as well as one having a prior type housing and has a construction that is inherently economical to produce and can be mass-manufactured in the large volumes required to supply original equipment converters directly to manufacturers of automobiles and trucks for factory installation in exhaust systems.
The present invention in preferred form involves the use of an open-ended oval metal tube. The catalyst coated ceramic substrate with a circumferential support mat is centrally placed inside of the oval tube. Thereafter, the central section of the oval metal tube is reduced in diameter to compress the mat and securely engage the substrate. During the diameter reducing process inwardly projecting longitudinal ribs are formed in the reduced section to maintain uniformity of reduction and mat compression. Annular raised ribs are formed near each open end of the tube and the open ends of the tube are pinched together by radial deformation to close the ends of the tube and form an inlet aperture in one end and an outlet aperture in the other end. In a preferred embodiment, the above procedure is used to position and secure two substrates in the housing, one being coated with three-way catalysts to convert nitrous oxides, carbon monoxide, and hydrocarbons and the other being coated with oxidation catalysts to convert carbon monoxide and hydrocarbons.
Other features and advantages of the invention will become apparent or be discussed in the detailed description.